The manufacture of digital optical media (i.e., discs) for the distribution of copyrightable content such as software, music, and movies, is becoming ever more common. Such a disc typically contains a version of copyrightable content created by the original author, artist, composer, etc., that has been digitized according to a predetermined format and stored in digital form (data) on the disc. The digital content of the disc can be read and converted into an output data stream (or ‘bit stream’), which, in turn, can be rendered in human-perceivable form (text, sound, images, etc.) and/or transferred to another data processing device, by a suitable read device (audio CD (Compact Disc) player, DVD (Digital Versatile Disc) player, disc drives, etc.). Thus, the output data stream represents the content stored on the disc. Some read devices may be associated with, and some include, writing capability for the writing of digital data to a writable disc. Such devices are also sometimes referred to as read/write devices or read/write drives.
Some of the most common industry standards for digitally encoding and decoding copyrightable content on optical discs are found in the ‘rainbow’ books, e.g., the Red Book for audio CD (Compact Disc Digital Audio System). The Red Book, initially promulgated by Philips and Sony corporations, sets forth technical specifications for CD and CD-ROM (Read Only Memory) formats, including the physical parameters and properties of the CD, the form of digital audio encoding (16-bit PCM), the optical “stylus” parameters, deviations and error rate, modulation system and error correction and other parameters. There is also a Yellow Book, which sets forth similar standards for the format of CD-ROMs, an Orange Book that defines formats for so-called writable and re-writable CDs (CD-R and CD-RW), a White Book for video CD formats, a Beige Book for photo CDs, and others. Most commercial read devices are configured to read data from, and/or write data onto, a disc in a format conforming to one or more of these standards. Such devices may be referred to as conforming devices, e.g., a conforming read/write drive, and may be said to be configured to read and/or write conforming data. Many of the physical and/or optical characteristics of the discs are tightly controlled to ensure the accurate and repeatable retrieval of the encoded digital data thereon. Variations in several of these characteristics will influence the performance of the data retrieval from the disc.
The ease with which conforming digital data can be copied has engendered a need for technological protection against unauthorized copying by copyright infringers. In particular, there is a need in the art for way to allow legitimate publishers of copyrightable content to generate identifying indicia on their discs in a manner that is not easily duplicated in copies made by infringers using conventional copying and reproducing techniques. One prior art attempt to identify legitimate discs has been to physically scribe or scratch a mark onto the disc in a predetermined place. Such markings, however, are difficult to precisely replicate on mass-produced discs and are easily detectable (and are therefore easy to counterfeit).